U.S. patent application Nos. '860 and '113, the disclosures of which are incorporated herein by reference, discloses and claims an improved wastewater treatment process referred to as I.D.E.A. "C.F.C.R." which is an acronym for "Intermittent Decant Extended Aeration Continuous Feed Cyclic Reactor" and incorporates CONTINUOUS FEED activated sludge technology with intermittent CYCLIC system operation requiring only a SINGLE BASIN. The system uses a single tank (reactor basin), preferably made of fiberglass in which the activated sludge is aerated over a number of pre-determined cycles. Solid/liquid separation occurs during the air-off cycle. Treated effluent is decanted or withdrawn from directly below the liquid surface. Influent inflow is continuously accommodated at all times. In this way the function of flow equalization, biological oxidation, nitrification, denitrification, secondary sedimentation and aerobic sludge digestion are all carried out in a single vessel. The duration of a cycle is specific to each design application and variable in the field as required.
The Continuous Feed Cyclic Reactor (C.F.C.R.) Process of the I.D.E.A. System combines SBR, ICEAS, and Continuous Flow Activated Sludge and Extended Aeration Principles. It is a fill and draw system which accommodates continuous feed (influent) to the tank (reactor basin). The heart of the process lies in the activated sludge blanket which reduces the BOD5 (biological oxygen demand) and TSS (total suspended solids) and removes nitrogen and phosphorous in the absence of polymers or filters. Food to microorganism ratios (F:M) may vary from 0.03 to 0.3 lb. of BOD5/lb of MLSS/DAY and mixed liquor suspended solids (MLSS) design concentrations range from 1,000 to 15,000 mg/l. Actual practice has shown MLSS concentration in the 2,000 to 8,000 mg/1 range to be most effective. With a hydraulic retention time (HRT) targeted for 18-36 hours and a sludge age (SRT) of at least 20 days. The Intermittent Decant Extended Aeration (I.D.E.A.) system is sized according to extended aeration standards. With such design parameters, typical excess solids (waste sludge) production ranges from 0.5 to 1.0 LB/LB of BOD5 removed. The sludge produced is quite stable with an insignificant (02) uptake rate and may be stored in a gravity sludge thickener without aeration or odors.
One of the major process advantages of the Intermittent or Cycled Extended Aeration Process (EPA Design manual "0n Site Waste-Water Treatment and Disposal Systems", October 1980.) used in the I.D.E.A. System is that it provides nitrification/denitrification in addition to carbonaceous BOD5 reduction and solids removal without the addition of methanol as an organic carbon source. In addition, denitrification enhances alkalinity recovery. This prevents a PH drop which could contribute to filamentous growth and bulked sludge. Alkalinity recovery is particularly advantageous in regions of low natural alklinity.
It is this unique cyclic process which allows the I.D.E.A System to accomplish nitrification and denitrificatioh. During aeration, biological oxidation and mixing occur. Blower sizing typically provides for 1.4 to 1.6 LBS. of (02)/LB of BOD applied/day. For very low strength waste, 20 SCFM/1000 cubic feet reactor volume is provided for mixing- During aeration, excess oxygen is present, and Nitrosomonas sp. oxidize the Ammonia Nitrogen (N/NH3) to Nitrite Nitrogen (N/NO2). Nitrobacter sp. further oxidize the Nitrite Nitrogen (N/NO2) to Nitrate Nitrogen (N/NO3). Both of these are naturally occurring bacteria as a result of this Intermittent or Cycled Extended Aeration "CFCR" Process.
Nitrate, Nitrite, Ammonia and Organic Nitrogen are all inter-related in wastewater. All of these forms of Nitrogen, as well as Nitrogen Gas are biochemically interconvertible. Ammonia is generally found in large quantities in fresh domestic wastewater, however Nitrate is found only in small amounts. But in the effluent of conventional Nitrifying biological treatment plants, Nitrate is found in concentrations of up to 50 mg/L Nitrate Nitrogen. Nitrite is an intermediate state of Nitrogen, both in the oxidation of Ammonia to Nitrate and in the reduction of Nitrate to Nitrogen Gas. Such oxidation occurs in the I.D.E.A System.
During non-aerated periods (sedimentation and decantation), the Dissolved Oxygen (DO) level in the sludge blanket (MLSS) approaches zero. The lack of molecular oxygen (O2) encourages Pseudomonas sp. and other denitrifying bacteria to attack the oxygen bound up in the Nitrate (NO3) molecules. The bacteria then reduce the Nitrate (NO3) molecules to nitrogen (N2) and oxygen (O2). The molecular Nitrogen (N2), a gas, is released to the atmosphere, while the bacteria utilize the liberated Oxygen (O2). Thus, alternation of oxic and anoxic periods in the I.D.E.A. basin promotes Ammonia Nitrogen (N/NH3) removal from the waste stream of 95% or better.
Additional Nitrogen removal is accomplished through assimilation (absorption and incorporation) of Nitrogen into bacterial cell mass in satisfaction of metabolic needs. This Nitrogen is removed from the system when excess sludge is wasted from the I.D.E.A. basin. Actual operating data have shown the concentration of nitrogen in the sludge mass to be between 5% and 8% by weight of the dry solids. As can be seen, the nutrient removals and high degree of treatment characteristic of tertiary treatment systems can be had at the cost of an I.D.E.A. "CFCR" secondary treatment system.
While the above mentioned patents clearly teach improved apparatus's none of these references deal directly with the problems associated with cyclic aeration and it is this problem that the present invention addresses.
In a draw and fill cyclic aeration system such as disclosed in the above references it becomes necessary to stir up the sludge blanket after the settle phase and this is done in several ways in the prior art.
One method is exemplified by U.S. Pat. No. 3,907,672 which uses an air diffuser line which is positioned along one side of the central chamber near the bottom of the tank to diffuse air into the chamber and to promote circulation. This system of diffusing air from a permanent manifold located near or on the bottom of a chamber to be aerated is standard and well known in the industry of wastewater treatment and has been used as a system of engineering choice in many facilities.
A second method of stirring up the sludge blanket is exemplified by U.S. Pat. No. 4,818,392 which uses a motorized fan to stir up the effluent by drawing the effluent upward creating currents to lift the sludge blanket.
A third alternative is taught by common usage prior art in which grid-shaped bottom aerators are suspended from a bridge structure extending transversely of a channel-type basin. In order to ensure adequate aeration of the active sludge over the full length of the basin, the bridge structure is mounted for reciprocating movement in the longitudinal direction of the channel. It is also suggested to attach the bottom aerators to a float which may be dragged through the basin without being supported by the bridge structure carried by the basin walls.
Basins of this type are constructed as so-called compact installations, but sometimes also as large scale installations. It has become evident, however, that a sufficiently safe control of the active sludge required for the sewage purification can be achieved in an economical manner only, if at all, in the case of the smaller compact installations. In the case of larger installations there is always the danger that the active sludge in certain areas dies off in an uncontrolled manner, leading to unstable conditions in the basin during the purification of sewage.
The smaller installations as well as the larger installations suffer from the disadvantage that their construction and operation are rather expensive. The treatment basins, which in most cases are concrete structures are expensive to build, and the mechanical installations for moving the bottom aerators and controlling the aeration process are complicated and subject to failure. In addition to high capital investment this results in high operating costs mainly due to high manpower costs.
The high investment and operating costs of an installation of this type frequently leads to several communities forming a joint venture, however, this necessitates the construction of sewers from the participating communities to the common sewage treatment plant. The costs of such sewers often exceed those of the treatment plant itself.
In view of these disadvantages, large-scale earthen basin installations with and without artificial aeration have been developed for plants serving up to about 10.000 PUV (population unit value). Pure earthen basins without artificial aeration have conventionally been built only for a few hundred PUV. In these basins there prevail undefined decomposition conditions between aerobic and anaerobic areas, so that an active sludge in the usual sense cannot develop. Since the absorption of oxygen takes place only at the surface, installations of this type have to have a very large surface area, and their operation in winter is unsatisfactory. The dwelling time of the sewage in these installations is usually 30 days and above.
The installations developed from such earthen basin installations and provided with line aerators or other devices, such as spot aerators are permitted to reduce the surface area requirements, however, they are still suffering from ill defined conditions as concerns their operation, resulting in dwelling times of domestic sewage of 10 to 20 days in the aerated sector, and of up to 30 days in the installation as a whole. In installations operating under higher load one has to accept extremely long dwelling times again requiring excessively large installations. While aerobic conditions prevail in certain areas of these installations, they are not controllable, and area with anaerobic conditions cannot be avoided.
Still another alternative is exemplified by U.S. Pat. No. 4,287,062 which teaches multiple bottom aerators which are connected to a flexible cable extending over the basin in such a manner that the aerators together with the carrier are periodically driven back and forth traversely of the longitudinal extent of the carrier by, it is claimed, the air exiting from the aerators. The flexible cable also requires floatation means to keep the cable and aerators afloat. This embodiment of an aeration system depends on currents in the aeration chamber created from the input to the output in the chamber and are under continuous activation. This system leaves the floatation device and carrier cable on the surface of the water and any objects floating on the surface water of a wastewater treatment system tend to accumulate unsightly and odorous sludge and debris, often times as much as 8 inches thick. This particular system is not feasible or satisfactory in a draw and fill system such as the present invention requires.
The present invention addresses these and other problems inherent in the above systems and while the above systems are somewhat successful for their own purpose, they are not satisfactory in the system as taught by the above referenced '860, '113 and co-pending application '976.